This invention relates to an improved processing method in which a measured amount of extrudate is severed by a cutting means and deposited in a receptacle traveling on a conveyor. The method of this invention is performed with an apparatus which is adaptable to crown making machinery, wherein a plurality of uniformly spaced crowns are positioned on a conveyor and a measured amount of molten extrudate is deposited in each crown to be formed into an insert liner and to molding equipment including a plurality of dies wherein the molten extrudate is formed into a prescribed configuration.
Heretofore, the quantity of extrudate material deposited in each crown was metered by controlling the rate of extrusion of the extrudate material and then directing this material through a cutting means timed to the feed rate of the crowns past the depositing station. In the case of molding equipment, a similar method was followed. The cutting means severs a metered charge from the extrudate material and propels the metered charge toward the depositing station at a velocity about equal to the tangential velocity of the cutting blade. In these prior art systems the cutting means comprises one or more cutting blades which continuously rotate at a constant tangential velocity, and the speed of the conveyor, feed rate of the extrudate material, cutting velocity of the cutting blade and velocity imparted to the metered charge are all proportional at a given rate of production. Thus, the lower feed rate of the crowns, the lower the cutting velocity of the cutting blade. For any rate of production, several variables must be interrelated, and the feed rate of the crowns must therefore be compatible with the cutting rate of the cutting means which must be compatible with the minimum cooling time of the formed liner.
An illustrative prior art apparatus is U.S. Pat. No. 3,827,843 to Blouch, wherein the cutting means has a knife blade which is rotated in synchronism with a conveyor such as a rotating conveyor. The motor which rotates the conveyor also rotates the knife blade on the cutting means via a belt drive and a chain drive which are selected to rotate the knife in timed relation to the conveyor. The knife blade moves continuously at a constant tangential velocity.
The prior art systems work well at high feed rates, such as above about 400 crowns per minute, where the cutting blade has a cutting velocity corresponding to 400 revolutions per minute of the cutting blade.
At lower feed rates, however, such as below about 400 crowns per minute, depending on the extrudate material being severed, the metered quantities of extrudate material are frequently not centered on the crown after being severed by the cutting means, and defective inserts result. That the metered quantities of extrudate material are centered on the crowns when the apparatus is operating at high production rates but are not centered at low production rates seems to indicate that the extrudate material absorbs the shock of the cutting means and elongates rather than being sheared at the cutting velocity of the cutting means for production rates below about 400 crowns per minute. These machines work most effectively only when the production rate is sufficiently high that the cutting means will have the minimum cutting velocity required to cleanly sever and propel the extrudate material toward the crowns without having the extrudate material absorb some of the shock and elongating, thereby affecting, among other things, the trajectory of the extrudate material as it drops downwardly to the crowns.
Each material fed through the extruder has a unique critical deformation rate below which it begins to elongate rather than being cleanly sheared, and this is an additional variable.